1. Field of the Invention
The present invention relates to a wired-circuit-board assembly sheet.
2. Description of the Prior Art
A suspension board with circuit mounted on a hard disc drive commonly comprises a metal supporting layer, an insulating base layer formed on the metal supporting layer, a conductive pattern formed on the insulating base layer, and an insulating cover layer formed on the insulating base layer for covering the conductive pattern. This suspension board with circuit is produced in the form of a suspension-board-with-circuit assembly sheet wherein a plurality of suspension boards with circuits are formed on a single sheet of metal supporting board.
Specifically, the suspension-board-with-circuit assembly sheet is produced in the manner that the insulating base layer, the conductive pattern, and the insulating cover layer are formed in sequence on a sheet of metal supporting board in the aligned state to correspond with each suspension board with circuit. Thereafter, the metal supporting board is sectionally cut out to correspond to an outline of each suspension board with circuit so as to form a suspension board with circuit and a supporting sheet for supporting the suspension board with circuit. Thus, the suspension board with circuit is produced in the form of a suspension-board-with-circuit assembly sheet wherein a number of suspension boards with circuit are formed in the aligned state on a single sheet of metal supporting board.
Then, each suspension board with circuit is properly cut off from the suspension-board-with-circuit assembly sheet for wide use in a variety of electric and electronic devices.
It is known that, in such suspension-board-with-circuit assembly sheet, defectiveness distinguishing marks are provided for each of the suspension board with circuit for distinguishing defectiveness of a marked suspension board with circuit.
For example, Japanese Unexamined Patent Publication No. 2000-151044 proposes that condemnation marks (the distinguishing marks) are formed in a wired-suspension-board sheet having wired suspension boards. These condemnation marks comprise a bridge of a very small width comprising a polyimide layer, a copper foil and a stainless steel foil, and a metal piece held by the bridge and are formed such as to correspond to each of the wired suspension boards. When a certain wired suspension board is judged to contain a broken wire, the condemnation mark for the related wired suspension board is taken out or removed by tearing off the bridge of the condemnation mark, while vacuuming up the metal piece of the condemnation mark in order to distinguish such a defective wired suspension board containing the broken wire from non-defective wired suspension boards by the removal of the condemnation mark (distinguishing mark).
However, this wired-suspension-board sheet described in Japanese Unexamined Patent Publication No. 2000-151044 has a problem that when the metal piece of the condemnation mark is removed, the bridge of the condemnation mark comprising the copper foil and the stainless steel foil is torn off, due to which metal powders of copper and stainless steel are easily generated, so that there is a possibility that the metal powders generated may adversely affect the electrical property of the wired suspension board.
Further, since the bridge comprises the copper foil and the stainless steel foil, it may be difficult to tear off the bridge by vacuuming.
On the other hand, when the metal piece of the condemnation mark is punched or stamped out using a metal stamp tool, although the bridge may be torn off with ease, however, the metal stamp tool is subject to abrasion by the friction between the copper foil and the stainless steel foil.